1. Field of the Invention
The present invention relates to a high pressure pump, which pressurizes fuel drawn into a pressurizing chamber through reciprocal movement of a plunger.
2. Description of Related Art
A high pressure pump, which pressurizes fuel drawn into a pressurizing chamber through reciprocal movement of a plunger, is known. For example, Japanese Unexamined Patent Publication No. 2002-521616A (corresponding to U.S. Pat. No. 6,345,608B) discloses a high pressure pump that has a valve member provided in a fuel passage, which is communicated with a pressurizing chamber, to adjust a flow quantity of fuel supplied to the pressurizing chamber. The valve member is driven by an electromagnetic drive device. The electromagnetic drive device reciprocates the valve member toward and away from a valve seat formed in a valve body through a needle. A stopper is provided on one side of the valve member, at which the pressurizing chamber is located. The stopper limits the movement of the valve member toward the pressurizing chamber.
In the high pressure pump of Japanese Unexamined Patent Publication No. 2002-521616A, at the time of metering the fuel supplied to the fuel chamber, the fuel flows from the pressurizing chamber toward the valve member. In this stage, the flow of the fuel collides against an end surface of the valve member located on the side of the valve member, at which the pressurizing chamber is located. At this time, the collision force of the fuel, which collides against the end surface of the valve member, may serve as an assist force that assists the movement of the valve member toward the valve seat. In such a case, unintentionally, the valve member may possibly be seated against the valve seat, thereby resulting in the unstable metering of the fuel. Specifically, the valve member is seated against the valve seat at the time, during which the valve member is supposed to be lifted away from the valve seat. That is, the unintentional valve closing (hereinafter, also referred to as self-closing of the valve member) occurs. Therefore, the quantity of fuel, which is pressurized in the pressurizing chamber, becomes unstable, and thereby the quantity and the pressure of the fuel discharged from the high pressure pump may become unstable. Another high pressure pump recited in Japanese Patent No. 3598610B does not have a means for blocking a flow of fuel from a pressurizing chamber toward a valve member, so that at the time of metering the fuel, the flow of fuel collides against an end surface of the valve member, which is located on the pressurizing chamber side of the valve member. Therefore, when a cam, which drives a plunger, is rotated at a low rotational speed, the valve member may possibly be self-closed, like the high pressure pump of Japanese Unexamined Patent Publication No. 2002-521616A. In such a case, the quantity of fuel discharged from the high pressure pump cannot be controlled.
Furthermore, in another high pressure pump recited in Japanese Patent No. 3833505B, a cup shaped valve member, which is engageable with a stopper, is provided, and an urging member is provided radially inward of the valve member. A plurality of fuel flow passages extends through a bottom portion of the stopper. The stopper has a sliding surface, along which the valve member slides. With this construction, the urging force of the urging member always acts along the sliding surface of the valve member. Therefore, even when the urging member is slightly tilted, the slide movement of the valve member is not disadvantageously affected. Furthermore, in the engaged state, in which the stopper and the valve member are engaged with each other, the fuel can flow into the interior of the valve member. Therefore, the pressure of the fuel in the interior of the valve member and the pressure of the fuel outside of the valve member can be the same. Therefore, at the time of intentionally closing the valve member with the electromagnetic drive device, it is possible to avoid an occurrence of a state where the valve member cannot be lifted away from the stopper. However, in the high pressure pump of Japanese Patent No. 3833505B, the fuel flows into the interior of the valve member even in the state where the stopper and the valve member are engaged with each other. Therefore, the flow of the fuel collides against the bottom portion of the valve member. As a result, even when the cam is rotated at the low rotational speed, the valve member may possibly be self-closed, like the high pressure pumps of Japanese Unexamined Patent Publication No. 2002-521616A and of Japanese Patent No. 3598610B.
Another high pressure pump of Japanese Patent No. 4285883B includes a valve member, which has an umbrella-like valve head and is engageable with a stopper. When the stopper and the valve member are engaged with each other, a volume chamber is formed between the stopper and the valve member. A plurality of fuel flow passages (notches or recesses) is provided in an outer peripheral part of an engaging portion of the stopper, which is engageable with the valve member. Furthermore, an outer diameter of the engaging portion of the valve member is set to be smaller than a diameter (also referred to as a width) of the engaging portion of the stopper. Therefore, at the time of metering the fuel, the flow of the fuel is blocked by the stopper and thereby does not collide against an end surface of the valve member, which is located on a side of the valve member where the pressurizing chamber is located. In this way, the self-closing of the valve member is limited, and it is possible to limit lowering of the self-closing limit of the valve member (i.e., the lower limit of the cam rotational speed, at which the self-closing of the valve member does not occur). Furthermore, a slit-like flow passage is provided in the contact surface between the stopper and the valve member. Thereby, in the engaged state where the stopper and the valve member are engaged with each other, the fuel can flow into the volume chamber through the flow passage. Thus, similar to the high pressure pump of Japanese Patent No. 3833505B, at the time of intentionally closing the valve member, it is possible to avoid the occurrence of the state where the valve member cannot be removed from the stopper. However, in the high pressure pump of Japanese Patent No. 4285883B, when the flow of the fuel collides against an opposed portion of the valve member, which is opposed to the flow passage at the time of flowing of the fuel into the volume chamber through the flow passage, a lateral force is exerted in the valve member (a force that is applied to the valve member in a direction perpendicular to an axis of the valve member). A shaft of the valve member, which extends in a direction away from the stopper, is slidably guided. Therefore, when the lateral force is exerted to the valve member, the lateral force is applied to the sliding portion of the shaft of the valve member. Thus, the sliding malfunction or abnormal abrasion of the shaft of the valve member may possibly occur. Also, the attractive force of the electromagnetic drive device, which attracts the valve member, may possibly need to be increased.